Variatichi of Temperature in the British Ides, &c. 67 



T/if Effect of the Types of Weatlier (Cyclonic or Anticydonic} on Tempera- 

 ture during fJte Five Years 1876-1880. 



The period from 1876 to 1880 was first examined. With the object 

 of classifying the days of this period, the atmospheric conditions pre- 

 vailing on each day were recorded on a separate card, to be subse- 

 quently grouped in any manner that might be thought desirable. The 

 conditions recorded were 



1. The mean temperature. 



2. The direction of the wind. 



3. The weather. 



4. The direction of the gradient (high to low), and 



5. The type of the weather prevailing (cyclonic or anticyclonic). 

 For this purpose weather was set down as cyclonic if the isobar on 



the 8 A.M. chart was concave to a region of low pressure, and as anti- 

 cyclonic if the isobar was concave to a region of high pressure. The 

 first classification was made according to the type of weather. It was 

 thought possible that this second-order temperature effect might be a 

 result of periodic variations in the relative frequency and effect of 

 cyclonic and anticyclonic weather at different periods of the year. 

 With the object of ascertaining whether this was the case,* the mean 

 temperatures and frequencies of occurrence of cyclonic and anticyclonic 

 weather, during each month of the year, were tabulated for the five 

 years under observation. For the purpose of examining the results, 

 curves of temperature were drawn whose ordinates are proportional, 

 not to the absolute mean temperature for the month, but to the 

 difference between the mean monthly temperature and the tempera- 

 ture which would be represented by the mean of the ordinates of the 

 first-order curve during the month ; so that the resulting curves show 

 that part of the temperature variations which is represented in the 

 harmonic analysis by a summation of all the curves of higher order 

 than the first. Diagram 2, fig. 1 (p. 68), shows these curves of tem- 

 perature for the cyclonic and anticyclonic days respectively. It will be 

 seen that only during the three summer months, and to a slight extent 

 during March, is the cyclonic weather cooler than the anticyclonic. 

 But both the curves show the main characteristics of the second-order 

 curve, viz., maxima in February and August, and minima in May and 

 November. Moreover, the curve of difference of temperature between 

 cyclonic and anticyclonic weather (fig. 2) shows three maxima in the 

 year. Fig. 3 shows the differences in frequency of the two types of 

 weather during each month, expressed as percentages of the whole 

 number of days in the month ; here again the curve is irregular, having 



* Mr. W. H. Dines, ' Quart Journ. Eoy. Met. Soc.,' vol. 23, p. 237, has already 

 given some reasons against regarding cold as definitely associated with anticyclonic 

 weather in winter. 



F 2 



